The goals of these studies are 1. To analyze the variability of mechanical properties of the lung during growth in terms of airway size as well as lung size and lung recoil and to relate this to some of the variations observed in the presentation of disease, 2. to study the effect of congenital anomalies upon the post-natal growth and development of the lung and 3. to develop, apply and interpret methods of assessing mechanics of respiration in children under 5 years of age. The hypothesis that individuals with high maximal expiratory flow have airways relative to their lung volume will be tested. Serial studies of airway size (estimated from measurements of anatomic dead space and tracheal cross-section area), elastic lung recoil (measured by volume-pressure curves) and of maximal expiratory flow-volume curves will be carried out to determine whether the variability in airway size is inborn or develops with growth. Infants born with diaphragmatic hernia have pulmonary hypoplasia. Our studies, using methods of respiratory mechanics and intrapulmonary distribution of Xenon 133, or adolescents successfully repaired in infancy show a reduction in pulmonary blood flow to the lung on the side of the hernia. The relationship of blood flow to lung volume is being explored. These same methods are being applied to determine the influence of the airway obstruction we have observed in adolescents with a lobectomy in infancy for congenital lobar emphysema on the distribution of ventilation and blood flow. Striking changes in the mechanical properties of the lungs take place during the first 5-7 years of life. Our objective is to apply techniques which require no cooperation (forced oscillations for resistance of the respiratory system, magnetometry for lung volume) to assess the mechanical properties of the lungs of small children in health and disease.